Legend:

[http://www.openscenegraph.org/documentation/OpenSceneGraphReferenceDocs/a01821.html osg::Viewport] is simply an encapsulation of glViewport. It is contained by a [wiki:Support/KnowledgeBase/Camera Camera]. You can read more about viewports and other OpenGL transformations [http://www.opengl.org/wiki/index.php/General_OpenGL:_Transformations here].